This invention relates to a reflex reflecting pavement marking sheet material and, more particularly, to a double layer pavement marking sheet material having excellent conformability to an irregular pavement surface.
Various sheet materials have heretofore been known as ones adhered to roadway for pavement marking purpose.
One type of such sheet materials is of a double layer structure as disclosed in U.S. Pat. Nos. 4,117,192, 4,248,932 and 4,282,281 in which a microsphere support layer holding a multiplicity of glass microspheres is bonded or coated on a base layer adhered to pavement surface. There is also known a type of such sheet material in which, as disclosed in U.S. Pat. No. 3,935,365, the base layer of such double layer structure is reinforced with cloth or the like reinforcing material.
The surface of pavement generally has irregular protuberances and depressions and a pavement marking sheet material is required to be a relatively soft one for conforming to such irregular pavement surface. In a case where the pavement marking sheet material is made of a single layer soft material, the surface of the sheet material tends to get soiled due to contact with tires of passing vehicle, dust tends to be deposited on the surface of the sheet material and, besides, glass microspheres disposed on the surface of the sheet material tend to be buried into the sheet material due to weight of the passing vehicle with resulting decrease in the reflecting effect. In the above described prior art double layer pavement marking sheet material, a glass microshere support layer made of a relatively hard resin such as hard PVC is provided for holding glass microspheres and preventing dust deposited on the surface of the sheet material. In this structure, the support layer holding the glass microspheres is so thin that the glass microspheres tend to come off in a relatively short period of time. Besides, since hard resin is coated on the surface of the sheet material, it takes time before glass microspheres embedded under the surface of the sheet material are exposed above the surface of the sheet material by the wear of the support layer so that reflection tends to be prevented for a long period of time before the glass microspheres are exposed.
In the prior art double layer pavement marking sheet material, the base layer which is made of material conformable to the irregular pavement surface is not sufficient in conformability to the pavement surface and is not free from the defect that the sheet material in some cases is separated from the pavement surface immediately upon release of pressure imposed upon the sheet material in application thereof on the pavement surface. For compensating for the irregularity of the pavement surface and thereby improving state of bonding of the pavement marking sheet material to the pavement surface, a primer is generally applied over a portion of the pavement surface on which the sheet material is to be bonded before the bonding of the sheet material is carried out. The application of primer however is still not sufficient for preventing such separation of the sheet material immediately after bonding thereof to the pavement surface. If the sheet material is separated from the pavement surface, the bonding ability of the sheet material is lost by reason by deposition of dust on the bonding surface of the sheet material or wetting of the bonding surface due to rain so that the sheet material will not be bonded to the pavement surface again with a result that there arises the likelihood that the sheet material collides with a tire of the passing vehicle and thereby is torn off.